Systems for rating a stick electrode

ABSTRACT

A system and method of rating the arc maintainability of an electric arc welding stick electrode by creating an arc between the electrode and a workpiece; moving the electrode along the workpiece while maintaining the arc; decreasing either the current or the voltage until a point is reached where the arc is extinguished; determining the open circuit voltage at the point; and, rating the electrode based upon at least the open circuit voltage point.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.11/879,564 filed Jul. 18, 2007, the disclosure of which is incorporatedherein by reference.

BACKGROUND

1. Technical Field

The subject matter discussed herein relates to the art of testing astick electrode and more particularly to a system and method of rating astick electrode as to the arc maintaining characteristic of theelectrode as determined by open circuit voltage.

2. Discussion of Art

Welding systems use stick electrodes that may vary in quality dependingon many variables. For example only, a stick electrode may vary inquality because of handling and or storage of the electrode by an enduser. It would therefore be desirable to develop a system and method torate an electrode so the quality of the electrode is known before use.

BRIEF DESCRIPTION

A system and method of rating the arc maintainability of an electric arcwelding stick electrode by creating an arc between the electrode and aworkpiece is disclosed. A stick electrode is moved along the workpiecewhile maintaining an arc therebetween. Either the current or the voltageis decreased until a point is reached where the arc is extinguished. Theopen circuit voltage at the point where the arc is extinguished isdetermined. The electrode is rated based upon at least the open circuitvoltage point. For example, in accordance with an embodiment, the opencircuit voltage is multiplied by the value of the arc current justbefore the arc is extinguished to obtain an energy rating number. Theenergy rating number is used as the rating of the stick electrode.

BRIEF DESCRIPTION OF THE DRAWINGS

Reference is made to the accompanying drawings in which particularembodiments of the invention are illustrated as described in more detailin the description below, in which:

FIG. 1 is an enlarged cross-sectional view showing a system set-up forconducting a method;

FIGS. 2 and 3 are schematic wiring diagrams of power sources used inperforming two different embodiments of the method and system;

FIG. 4 is a graph illustrating performance of the method, primarily whenthe welding is DC positive and where rating is accomplished bydecreasing the arc current;

FIG. 5 is a table tabulating the results of the test performed inaccordance with FIG. 4;

FIG. 6 is a flow chart of the program to perform the method shown inFIGS. 4 and 5;

FIG. 6 a is a schematic of a circuit for determining and recordingcurrent and voltage;

FIG. 7 is a graph illustrating another embodiment utilizing a constantcurrent concept for AC and DC positive welding, wherein OCV points arelocated for use in plotting a curve representing the characteristics ofa stick electrode;

FIG. 8 is a graph of voltage versus current for several different stickelectrodes using an analysis of the results as illustrated in FIG. 7;

FIG. 9 is a table tabulating the results of the rating procedure andmethod of FIGS. 7 and 8;

FIG. 10 is a table tabulating a further analysis step as described inFIGS. 7-9;

FIG. 11 is a flow chart of the program to perform the methodschematically illustrated in FIGS. 7-10; and,

FIG. 12 is a voltage current graph illustrating a simplified embodimentof the method for rating a stick electrode.

DETAILED DESCRIPTION

Embodiments relate to a system and method of rating a stick electrode.With reference to the drawings, like reference numerals designateidentical or corresponding parts throughout the several views. However,the inclusion of like elements in different views does not mean a givenembodiment necessarily includes such elements or that all embodiments ofthe invention include such elements.

A quality characteristic of a stick electrode is its ability to maintainan arc at low heat energy. This is also expressed as a low open circuitvoltage. Indeed, this characteristic of maintaining an arc at low energyis more critical in an electrode which contains a fluxing system,because such system affects the arc stability and makes it moredifficult to maintain an arc or plasma at a high arc length. The systemand method relate to rating a stick electrode having an outside coatingwith a flux system, such as a rutile fluxing system.

The system and method relate to rating a stick electrode E for itsability to maintain an arc at low voltages and/or low currents. This isalso expressed as low wattage and/or low power. The rating fixture orset-up 10 involves an elongated simulating pipe joint defined by gap 12and upper groove 14 formed by two spaced plates 20, 22 representing pipesections. Stick electrode E is schematically illustrated in FIGS. 1-3and includes an integral fluxing system, e.g., a rutile fluxing system.Set-up fixture 10 is used to rate the arc maintaining capabilities ofstick electrode E, which ability is an important quality characteristicof a stick electrode used in manual welding. Rating a stick electrodeinvolves the ability of the electrode to maintain arc A as the voltageor current is decreased in a manner schematically illustrated in FIG. 2or when the voltage is decreased as shown in FIG. 3. These two figureseach illustrate a standard power source 30 driven by power supply 32 tocreate waveforms across output leads 34, 36 connected to electrode E andworkpiece WP. In FIG. 2, the power source controller includes thecapability of decreasing, in gradual increments, the arc current andrecording such decrements as indicated by device 40. In a like manner,as shown in FIG. 3, the controller of power source 30 includes a device42 for decreasing gradually and recording changes in voltage. Devices40, 42 of FIGS. 2 and 3, respectively, are used in performing differentembodiments of the system and method.

In accordance with an embodiment, when welding in DC positive, thetesting procedure set forth in FIG. 4 is normally employed whereindevice 40 gradually decreases the arc current so a deposition ratedecreases along curve 50 from a high starting point 52. As electrode Eis moved along groove 14 for welding in the joint between plates 20, 22,device 40 continues to decrease the welding current until arc A isextinguished at OCV point 54. At that point, the open circuit voltage ofpower source 30 is recorded. This is accomplished by device 60 shown inFIG. 2 wherein the arc voltage is detected by circuit 62 so that theopen circuit voltage at point 54 appears as digital information onoutlet line 62 a. The open circuit condition is sensed by shunt 64,which indicates zero current in line 66 when the arc has beenextinguished at point 54. Thus, at point 54 recording device 60, e.g., aprogram or circuit, records a digital number indicative of the opencircuit voltage at point 54. As shown in column 72 the area of theparticular electrodes being rated is recorded. In another embodiment,more than one electrode of each type is tested by the method shown inFIG. 4. The number in column 72 is the average open circuit voltage OCVfor all electrodes of a given type being rated. Thus, the rating of anelectrode is the average open circuit voltage OCV, which average numberor value is exhibited in column 74. The number, in digital format, isused for expressing the arc stability characteristic of electrode E asrated by the present method. This rating method is performed by program80 shown in the flow chart of FIG. 6. In this program the electrode tobe rated is selected as step 82. The arc current is decremented, asshown in FIG. 2 and represented by step 84. When the point 54 has beenreached, the open circuit voltage is identified and recorded by deviceor program 60, which constitutes step 86. In one embodiment, thisconcludes the actual rating procedure. In another embodiment, severalelectrodes are processed to obtain an average open circuit voltage. Thisis indicated at step 90 wherein several electrodes A are processed toobtain several points 54. The total value of the several values for theopen circuit voltage at points 54 of the electrodes is averaged asindicated in FIG. 5, and represented at step 92 in FIG. 6. Program 80assigns a rating number to the electrode as indicated at step 94. Thisrating number is recorded in column 74 of FIG. 5 to evaluate the arcmaintaining capabilities of various competitive electrodes. The methodmay use the machine of FIG. 2 to perform the procedures illustrated inFIGS. 4-6; however, other methods can be used for determining the lowenergy arc stability of a stick electrode.

Converting the open circuit voltage value at point 54 into an energyrating number is accomplished by circuit EC in FIG. 6A. Circuit EC isused to determine and record the combination of the current and opencircuit voltage when the arc is extinguished at point 54. The lowestenergy required to maintain an arc is determined by circuit EC where thecurrent on line 66 is directed to a holding circuit 100, so output line102 has a number representing the current at point 54. This number isone input to multiplier 110. The other input is a number representingthe open circuit voltage at point 54. The second number appears on line62 a. These two numbers or values are multiplied to provide a wattcalculation on line 112. This calculation gives a digital numberreferred to as the “energy” rating number and it is recorded in register120. Thus, after performing the rating method illustrated in FIG. 4,resulting data from FIG. 2 is processed by circuit EC to give an energyrating for electrode E. The electrode will lose its welding arc at anenergy below the energy recorded in register 120. This recorded numberis a stability characteristic of electrode E. It indicates the abilityto withstand large arc lengths and deviations in arc current. The ratingmethod is described in FIG. 4 and an evaluation technique for this datais performed by circuit EC of FIG. 6A.

Another embodiment for rating a stick electrode by the power or energythat will no longer sustain an arc is illustrated in FIGS. 7-11. Thisembodiment is especially applicable for AC welding and DC negativewelding and uses the machine schematically shown in FIG. 3. This machinehas the features of the machine in FIG. 2 with device 42 forincrementally reducing the welding voltage while maintaining the weldingcurrent constant. This embodiment of the invention is schematicallyillustrated in FIG. 7 where the rating method generates graph 150. Thisgraph is created by holding the welding current constant at a givenvalue and then decreasing the arc voltage by device 42. The arc voltageis directed to program or device 60 from voltage detector 62 on line 62a. A series of procedures are performed in rating electrode E. Theseprocedures each involve holding the arc current constant and reducingthe arc voltage until the arc energy does not sustain the plasma columnor arc. These procedures are shown as separate procedures 150 a-150 g todetermine the points a-g at which the energy of the arc is insufficientto maintain the arc. Consequently, at each current of the procedures 150a-150 g an open circuit voltage point a-g is determined. These pointsare plotted as curve 200 of FIG. 8 for electrode E1. This curve isplotted by using the data created by the method described in FIG. 7.Testing of electrode E1 generates data points to plot curve 200. Otherelectrodes E2, E3 are processed by the method in FIG. 7 to plot curve202 and curve 204, respectively. These curves have an integrated area210 under the curve, which area encompasses all energy levels where theelectrode cannot sustain an arc. Each energy level is a product ofcurrent and voltage and is the same as the output of circuit EC shown inFIG. 6A. Consequently, the area under the curves determine the qualitycharacteristic of each electrode. The area represents the ability tosustain a welding arc at low energy levels. Areas A1, A2 and A3 are setforth in column 222 of table 220 as they relate to and correlate withelectrodes E1, E2 and E3 in column 222 of table 220. The evaluation ofthe electrodes as compared to each other is the numerical valueestablished by the area under the curve shown in FIG. 8 and is recordedon table 220 in FIG. 9. In another rating procedure using calculatedareas, the different electrodes are compared by a program performing thealgorithm of the conversion chart 230 in FIG. 10. Several electrodes areprocessed in accordance with the method in FIG. 7 to establish the areaunder the plotted curve, as disclosed in FIG. 8. The summation of all ofthese areas for a given electrode is then divided by the number ofelectrodes tested. This data manipulation generates a digital numberrecorded in column 236 of chart 230. The recorded number relates to theelectrodes in column 232 by executing the intermediate calculation incolumn 234. The relative quality of the individual electrodes is thenumber in column 224 of table 220 or the number in column 236 ofconversion chart 230. This rating technique or method is performed,using the basic concept shown in FIG. 4 as further set forth andmodified in FIG. 7.

A flow chart of program 300 for the embodiment shown in FIG. 7 is shownin FIG. 11. Step 302 involves selecting the electrode to be evaluated.At step 304, a constant current is maintained at one of the severalprocedures set forth in FIG. 7. At step 306, the arc voltage isdecreased by device 42 shown in FIG. 3 to create one of the “out” pointsa-g of graph 150. As illustrated in FIG. 8, step 310 involves plottingthe curves 200, 202 or 204 based upon the determined open circuit pointsa-g. At step 312, the area under a curve is calculated by an algorithm,as explained in connection with table 220. This process step assigns arating number at step 314. This rating number is either the area ofcolumn 224 in FIG. 9 or the calculated number for the average area incolumn 236 of FIG. 10. FIGS. 7-10 illustrate the basic concept ofreducing either the current or the voltage to determine the open circuitvoltage or the point in which the arc energy will not sustain an arc.This determination of the open circuit voltage or arc sustaining energyis expressed in an assigned number to rate the quality of the electrode.In alternative embodiments, there are other processes for employing theconcept of measuring the sustaining power or energy of the arc for agiven electrode to rate an electrode.

The procedure in FIG. 4 is a single procedure wherein the current isreduced until the arc plasma is no longer sustained. This same simpleone step procedure is used many times in the rating method of FIG. 7.This one step concept is schematically shown in FIG. 12 whereinprocedure 350 is like one of the several procedures 150 a-150 g. The arccurrent is held constant at a value K and the arc voltage is reducedalong line 352 until the arc is extinguished at point 354. This is themethod of FIG. 4, but using voltage. These procedures determine thewattage, or more simply the open circuit voltage, at which the arc is nolonger sustainable. This value is used in determining the quality of astick electrode.

In summary, an embodiment of the present invention comprises a method ofrepresenting arc maintainability of an electric arc welding stickelectrode for depositing molten metal from the electrode onto aworkpiece by using an arc between the electrode and the workpiece,wherein the arc is caused by a voltage from a power source where thevoltage creates a current of the arc. In accordance with an embodiment,the stick electrode has an outer coating containing a fluxing system,and the fluxing system is rutile based. The method includes creating thearc between the electrode and the workpiece and moving the electrodealong the workpiece while maintaining the arc. The method furtherincludes decreasing either the current or the voltage until a point isreached where the arc is extinguished, wherein the point corresponds toan open circuit voltage, and wherein the open circuit voltage is thevoltage at the point where the arc is extinguished with a zero currentvalue which corresponds to the current of the arc at the point where thearc is extinguished. The method also includes determining an opencircuit voltage of the power source at the point where the arc isextinguished and rating the electrode by multiplying the open circuitvoltage by a current of the arc just before reaching the point where thearc is extinguished to obtain an energy rating number. The step ofdecreasing may relate to the current of the arc or the voltage of thearc. The voltage may be one of a DC positive voltage, a DC negativevoltage, or an AC voltage. The rating step may further include obtainingthe point for N electrodes, adding the energy rating numbers of the Npoints to obtain a total, and using the total to rate the electrodes.The total may be divided by N before being used to rate the electrodes,in accordance with an embodiment.

Another embodiment of the present invention comprises a system. Thesystem includes a power source, an electrode and a workpiece, and outputleads electrically connecting the power source to the electrode and theworkpiece. The system also includes an arc voltage detecting circuit, anopen circuit detecting circuit, and a power source controller. Thesystem further includes a recorder configured to record at least an opencircuit voltage, wherein the open circuit voltage is the voltage at apoint where the arc between the electrode and the workpiece isextinguished. The system also includes an energy circuit that determinesan energy rating number for the electrode based on the open circuitvoltage and an arc current. The current is determined just before apoint where the arc is extinguished. In accordance with an embodiment,the power source controller is configured to decrease an arc current ingradual increments and the recorder is configured to record the arccurrent. The recorder is configured to record the arc current at a pointjust before the arc is extinguished, and the electrode is rated basedupon the open circuit voltage and the arc current. In accordance with anembodiment, the power source controller is configured to decrease avoltage in gradual increments and the recorder is configured to recordthe voltage. In accordance with an embodiment, the energy rating numbermay be graphically represented in at least one curve, and an area underthe at least one curve may be used as a quality rating for theelectrode.

While the claimed subject matter of the present application has beendescribed with reference to certain embodiments, it will be understoodby those skilled in the art that various changes may be made andequivalents may be substituted without departing from the scope of theclaimed subject matter. In addition, many modifications may be made toadapt a particular situation or material to the teachings of the claimedsubject matter without departing from its scope. Therefore, it isintended that the claimed subject matter not be limited to theparticular embodiments disclosed, but that the claimed subject matterwill include all embodiments falling within the scope of the appendedclaims.

What is claimed is:
 1. A system comprising: a power source; an electrodeand a workpiece; output leads electrically connecting said power sourceto said electrode and said workpiece; an arc voltage detecting circuitconfigured at an output of the power source to detect an output voltageproduced by the power source that is applied between the electrode andthe workpiece through the output leads; an open circuit detecting shuntconfigured at an output of the power source to detect an output currentproduced by the power source that flows through the output leads andbetween the electrode and the workpiece when an arc is formed betweenthe electrode and the workpiece; at least one of an output currentdecreasing device and an output voltage decreasing device configured tocommand the power source to decrease either the output current or theoutput voltage until a point is reached where the arc is extinguished,wherein the point corresponds to an open circuit voltage, and whereinthe open circuit voltage is the voltage at the point where the arc isextinguished with a zero output current value which corresponds to theoutput current of the arc at the point where the arc is extinguished; arecorder configured to record at least the open circuit voltage, whereinsaid open circuit voltage is the voltage at the point where the arcbetween the electrode and the workpiece is extinguished with the zerooutput current value being zero which corresponds to the current of thearc at the point where the arc is extinguished; and an energy circuitconfigured to determine an energy rating number for said electrode basedon said open circuit voltage and an arc current and assign and outputdigital information representative of the energy rating number.
 2. Thesystem as defined in claim 1 wherein said output current decreasingdevice is configured to decrease an arc current in gradual incrementsand said recorder is configured to record said arc current.
 3. Thesystem as defined in claim 2 wherein said recorder is configured torecord said arc current at a point just before said arc is extinguished,and wherein said electrode is rated based upon said open circuit voltageand said arc current.
 4. The system as defined in claim 1 wherein saidoutput voltage decreasing device is configured to decrease a voltage ingradual increments and said recorder is configured to record saidvoltage.
 5. The system as defined in claim 1 wherein said arc current isdetermined just before a point where said arc is extinguished.
 6. Thesystem as defined in claim 1 wherein said energy rating number isgraphically represented in at least one curve, and wherein an area underthe at least one curve is a quality rating for said electrode.